topic
Everyone knows the Fibonacci sequence, and now requires an integer n, please output the nth item of the Fibonacci sequence (starting from 0, the 0th item is 0), n <= 39.
Recursive implementation
public class Solution {
public int Fibonacci(int n) {
if( n <= 1){
return n;
}
return Fibonacci(n-1) + Fibonacci(n-2);
}
}
Optimize recursion
public class Solution {
public int Fibonacci(int n) {
int ans[] = new int[40];
ans[0] = 0;
ans[1] = 1;
for(int i=2;i<=n;i++){
ans[i] = ans[i-1] + ans[i-2];
}
return ans[n];
}
}
Optimize storage
public class Solution {
public int Fibonacci(int n) {
if(n < 2){
return n;
}
int one = 0;
int two = 1;
int sum = 0;
for(int i = 2; i <= n; i++ ){
sum = one + two;
one = two;
two = sum;
}
return sum;
}
}